1. The Field of the Invention
The present invention relates to a vehicle air pressure maintenance systems. More specifically, the invention relates to a self-contained tire pressure maintenance and monitoring system powered by a fluid fly-wheel generator.
2. Technical Background
Monitoring and maintaining proper tire air pressure for vehicles has long been an important maintenance item carried out by a vehicle owner. Early on, tire pressure was checked regularly because low pressure tires were easily noticed. However, as tire technology has advanced low pressure tires are harder to spot by simple observation. This, and a perception that more advanced tires experience fewer slow leaks, has lead vehicle owners to stop or drastically reduce monitoring of tire pressure for their vehicles.
Tires are still subject to leaks. Generally, the leaks are slow and may not always completely deflate the tire. The leaks may be caused by failed tire valves, an opening between the tire and rim, or a puncture of the tire or inner tube by a foreign object such as glass or a nail. Natural leaks may reduce the pressure by as much as 1 pound per square inch (psi) per month. Seasonal temperature changes also reduce tire pressure by 1 psi for every drop of 10 F. degrees in temperature. Changes in altitude also affect tire pressure.
Low tire pressure may cause significant problems. Studies relied upon by the National Highway Traffic Safety Administration (NHTSA) indicate that low pressure tires reduce vehicle safety. For example, lower pressure causes more wear on the tire sidewalls which may lead to premature failure. The NHTSA estimates that 23,464 crashes were a result of under inflated tires.
Low tire pressure also reduces the life of the tire. Data from Goodyear and Michelin indicate that tires which are 20% under inflated can reduce the tires life by up to 50%. Low tire pressure causes the tire tread to wear non-uniformly which may also cause premature failure of the tire. Tire costs, particularly for the trucking industry, are the second highest maintenance expense behind fuel. Tire costs even exceed the cost for drivers of the trucks.
Low tire pressure reduces the fuel economy for the vehicle. Tires with lower pressure require more energy to turn. Goodyear indicates that tires that are 15% under inflated result in 2.5% increased fuel consumption.
In response to these problems caused by low tire pressure, efforts have been made to provide devices and systems which monitor and/or maintain the tire pressure in a vehicle""s wheels. The pressure maintenance efforts have focused on mechanisms for adding small amounts of air to the tire while the tire rotates to compensate for losses due to leaks.
These devices are often attached to the tire and/or the axle of a wheel. However, some systems interfere with the normal operation of the tire. Devices attached to the axle generally must be removed before the rim or brakes of a particular wheel may be accessed.
Other devices leverage the centripetal force generated by the turning wheel to drive mechanical pumps. The devices are generally attached to the axle or the rim of the wheel. However, these devices are often expensive and may require constant maintenance to ensure proper operation. Furthermore, these devices often fail to monitor the tire pressure to notify a vehicle driver of low pressure tires.
Conventional devices generally do not compensate for changes in altitude or ambient air temperature. Devices which do allow for altitude or temperature compensation, may often require manual adjustment to compensate. Furthermore, the complexity and relatively high number of moving parts lead to higher maintenance and repair costs for the devices.
Other conventional devices for maintaining air pressure are not xe2x80x9cfail-safexe2x80x9d meaning failure of the devices can directly cause the tire to fail. For example, the device may continue adding air when the proper pressure is reached, thereby causing a blow-out. Alternatively, the components of the device may fail and cause more air to leak than normally would without the device.
Finally, a federal government agency is proposing to require tire pressure monitoring systems on all new cars, trucks, and multipurpose passenger vehicles. (See xe2x80x9cTire pressure monitoring systems; controls and displaysxe2x80x9d NHTSA, 49 CFR Part 571) This proposal would require tire pressure systems to notify the driver of low pressure tires below a threshold level. Such a proposal may be very costly if conventional tire pressure maintenance and monitoring systems must be used and maintained (replacement of batteries, etc.).
Accordingly, it would be an advancement in the art to provide a tire pressure maintenance and monitoring system which is powered by a simple fluid fly-wheel generator. It would be a further advancement to provide a tire pressure maintenance and monitoring system which is reliable, and inexpensive to produce. Additionally, it would be an advancement in the art to provide a tire pressure maintenance and monitoring system which does not interfere with the axle or tire and does not cause the tire to fail if the system fails. The present invention provides such a system in a novel and useful way.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available tire pressure maintenance and monitoring devices. Thus, the present invention provides a tire pressure maintenance and monitoring system which is simple, inexpensive, self-contained, and fails safely.
In one embodiment, the tire pressure maintenance and monitoring system includes a simple fluid fly-wheel generator. The fluid fly-wheel generator includes a sealed tube. Preferably, the tube is a toroid shape which rotates about a central axis. In certain configurations, the tube may be fixed to a rim of a vehicle wheel.
A fluid, preferably hydraulic fluid, within the tube is free to circulate through the tube. The fluid flows within the tube when the tube accelerates about the axis. As the tube accelerates rotationally, the inertia of the fluid causes the fluid to flow in the opposite direction of the tube""s rotational acceleration.
A turbine within the tube is turned by the flow of the fluid. In one configuration, the turbine transfers the inertia of the fluid into mechanical energy to drive a mechanical pump or electric generator. Alternatively, the turbine may include magnetic poles and be configured to rotate about a lateral axis to induce a current in wire coils. The tube, fluid, and turbine cooperate to form a xe2x80x9cliquid fly-wheel.xe2x80x9d
In one embodiment, the turbine of the liquid fly-wheel may be magnetized to generate a magnetic field. External to the tube and in close proximity to the turbine a pair of opposing wire coils may be saddled around the tube within the magnetic field. The rotating turbine generates an electric current in the windings through induction.
In another embodiment, the liquid fly-wheel powers a mechanical pneumatic pump. The turbine may be coupled to a spur gear which turns a crank to drive a pneumatic piston when the turbine turns. In addition, the piston may be biased by a temperature sensitive spring to control the piston movement based on the ambient temperature. The pneumatic pump may also include check valves to control when pumped air may enter the tire. These check valves may discharge the pumped air when the tire pressure reaches a pre-determined level.
In certain embodiments, the turbine of the liquid fly-wheel may be coupled to various electrical and/or mechanical components to provide a tire pressure maintenance and monitoring system. In one configuration, the liquid fly-wheel is coupled by a shaft to an electric generator. The turbine of the liquid fly-wheel turns the shaft to power the electric generator which produces a current.
In one embodiment, the tire pressure maintenance and monitoring system may be wholly contained within a vehicle wheel. The liquid fly-wheel and electric generator may be fixed to the outer edge of a rim within the tire walls. The electric current may be stored within a battery or capacitor fixed to the rim or used directly to power an electric pneumatic pump also attached to the rim. The electric pump may draw current from the battery, capacitor, and/or the electric generator. The pump may be controlled by a pressure sensor which activates the pump when the air pressure drops below a pre-determined level. Alternatively, the pump may be controlled by a logic system which actuates the pump based on other factors. For example, the logic system may actuate the pump based on a pre-determined wheel speed.
The tire pressure maintenance system may also include a controller coupled to the pump, a temperature sensor and an altitude sensor in communication with the controller. The controller may periodically monitor readings from the temperature sensor, altitude sensor, and pressure sensor. Based on the readings, the controller may automatically control the electric pump to regulate the air pressure within the tire. Furthermore, the controller may transmit the readings by radio signals from a first transceiver to a second transceiver external to the vehicle wheel. Of course signals representing the readings may be sent through induction or optical couplings as well. The second transceiver may communicate the signals to a vehicle control system (VCS). Based on the signals, the VCS may provide a notification to a driver of the condition of the air pressure within one or more vehicle tires. In one configuration, a display light is illuminated to indicate a tire with low air pressure.
The tire pressure maintenance system may also include an electric charge sensor for monitoring an amount of charge in the battery. The electric charge sensor being coupled to the battery and the controller. The controller may use readings from the electric charge sensor to maintain a level of charge in the battery to a minimum level. The minimum level may be at least enough charge to allow the system to transmit current tire pressure readings to the second transceiver. Thus, the battery is continuously being re-charged. In this manner, a driver is at least notified of the current tire pressure readings and can take appropriate action.